Abstract: Supplemental O2 therapy and non-invasive ventilation (e.g. continuous positive pressure support, CPAP) are two major life-saving modalities of respiratory care for the treatment of preterm infants with respiratory distress syndrome. Unfortunately, there are significant unintended consequences associated with clinical care. Supplemental O2 therapy specifically has long been recognized as a potent contributor to the pathogenesis of wheezing and asthma of former preterm infants ? these observations have led to efforts to titrate and minimize the usage of O2 in the NICU setting and a shift toward increased use of CPAP. The dilemma, however, is that virtually nothing is known about whether there are also any adverse side-effects of CPAP. In this proposal, we will utilize a novel neonatal mouse model of CPAP (developed in our lab) to test the hypothesis that there are indeed, long-term adverse consequences associated with CPAP, manifest as an increase in airway hyperreactivity (AHR). We further hypothesize that the mechanistic basis underlying the effects of CPAP on AHR involves a stretch-induced increase in low-molecular weight hyaluronan (HALMW) expression in airway smooth muscle. HALMW is a major component of the extracellular matrix and our data show that it initiates downstream signaling pathways leading to increased calcium signaling, hyperreactivity, and smooth muscle proliferation. In parallel studies, we also show that the HA- Ca2+ pathway is functional in age-appropriate (for preterm infants) human fetal airway smooth muscle cells. Interestingly, offsetting or counter-balancing the increased HALMW by exogenous delivery of high molecular weight HA (HAHMW) prevents the adverse effects of CPAP. The clinical safety of HAHMW has been tested in a variety of settings ranging from treating eye abnormalities in preterm infants to children with cystic fibrosis, and adults with asthma. Therefore, this proposal will utilize a novel mouse model of neonatal CPAP to highlight the mechanistic basis for the unintended consequences it has on airway function, and provide evidence demonstrating tremendous promise for HAHMW administration as a viable therapy for the treatment and prevention of wheezing and asthma in former preterm infants.